This invention relates to a method of manufacturing a large area active matrix array for a large area imaging or display device.
Active matrix display devices such as liquid crystal (LCD) displays and matrix addressed image sensors using thin film technology have many applications some of which may require an active matrix array of large area, for example a 20 cm (centimeter) by 20 cm or even a 40 cm by 40 cm array. Such large area arrays may be required where, for example, an image sensor is to be used in medical applications, for example as part of an X-ray detector, or in large document imaging for example in electronic copying or facsimile machines.
It is currently not technically feasible to manufacture such a large area active matrix array on a single substrate because even where machines are available to enable deposition and patterning of layers over such a large area, the possibility of defects occurring increases markedly with area and thus the likelihood of some areas of the array not functioning correctly is very high. The yield of correctly functioning arrays would therefore be extremely low.
JP-A-63-183420 describes an LCD display having a transparent first base plate carrying transparent scanning electrodes. A number of transparent second base plates are provided each carrying an array of pixel electrodes and a matrix of switching elements in the form of electrodes running along the length of the second base plate. The second base plates are bonded to a third base plate so as to be joined together in a direction perpendicular to the scanning electrodes. The liquid crystal is sandwiched between the first and second base plates. In the LCD device described in JP-A-63-183420 each of the second base plates extends across the entire width of the array and accordingly the manufacture of this device requires the deposition and patterning of the materials for forming the thin film diodes and pixel electrodes over an area which still has a width equal to that of the desired array. Thus, the problems of the low yields which are obtainable when depositing and patterning materials over a large area still remain.